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authorWaiman Long <longman@redhat.com>2018-10-18 21:45:17 -0400
committerIngo Molnar <mingo@kernel.org>2018-10-19 07:53:17 +0200
commit9506a7425b094d2f1d9c877ed5a78f416669269b (patch)
tree7eacd4d0a4dcc8ffffd2384d9e75624bbbe86e86 /kernel
parent0fa809ca7f81c47bea6706bc689e941eb25d7e89 (diff)
locking/lockdep: Fix debug_locks off performance problem
It was found that when debug_locks was turned off because of a problem found by the lockdep code, the system performance could drop quite significantly when the lock_stat code was also configured into the kernel. For instance, parallel kernel build time on a 4-socket x86-64 server nearly doubled. Further analysis into the cause of the slowdown traced back to the frequent call to debug_locks_off() from the __lock_acquired() function probably due to some inconsistent lockdep states with debug_locks off. The debug_locks_off() function did an unconditional atomic xchg to write a 0 value into debug_locks which had already been set to 0. This led to severe cacheline contention in the cacheline that held debug_locks. As debug_locks is being referenced in quite a few different places in the kernel, this greatly slow down the system performance. To prevent that trashing of debug_locks cacheline, lock_acquired() and lock_contended() now checks the state of debug_locks before proceeding. The debug_locks_off() function is also modified to check debug_locks before calling __debug_locks_off(). Signed-off-by: Waiman Long <longman@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Will Deacon <will.deacon@arm.com> Link: http://lkml.kernel.org/r/1539913518-15598-1-git-send-email-longman@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/locking/lockdep.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index be76f476c63f..1efada2dd9dd 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -4066,7 +4066,7 @@ void lock_contended(struct lockdep_map *lock, unsigned long ip)
{
unsigned long flags;
- if (unlikely(!lock_stat))
+ if (unlikely(!lock_stat || !debug_locks))
return;
if (unlikely(current->lockdep_recursion))
@@ -4086,7 +4086,7 @@ void lock_acquired(struct lockdep_map *lock, unsigned long ip)
{
unsigned long flags;
- if (unlikely(!lock_stat))
+ if (unlikely(!lock_stat || !debug_locks))
return;
if (unlikely(current->lockdep_recursion))